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OPA2991: OPA2991 as a Comparator

Tom Chen

Prodigy 10 points

Part Number: OPA2991

Tool/software:

OPA2991 as comparator with V+=+5V V- = -5V In+ =2.5V , In- =0 V,The Out 4.99V work, but The In- Pin has hundred uA current if ground to 0V, ref to datasheet the input current should be low more than this.

0 Clemens Ladisch 9 months ago

Guru 295730 points

This should not happen.

What resistance between IN− and V+/V− do you measure with the chip unsoldered and unpowered? Anything lower than approximately infinity would indicate a damaged device.

0 Ron Michallick 9 months ago

TI__Guru**** 156616 points

Hello Tom, welcome to the e2e forums.

Make sure pin 4 is really -5V and not accidently disconnected. If pin 4 is open then the lowest voltage pin will try to take pin4's place.

If IN- is greater than 2.5V, what is the pin current and output voltage?

0 Tom Chen 9 months ago in reply to Ron Michallick

Prodigy 10 points

if In- Greater Than 2.5V,output is -4.99V, but In- Pin current is not acceptable

0 Tom Chen 9 months ago in reply to Clemens Ladisch

Prodigy 10 points

test PIN4 is -5V measured by DMM

+1 Tom Chen 9 months ago in reply to Tom Chen

Prodigy 10 points

Solved,There is a fake chip on the picture bottom,The Upper One all is ok.